System for contact-free, axially stabilized and radially centered positioning of a rotating shaft, particularly of an operating machine for low temperatures

ABSTRACT

A system for contact-free, axially stabilized and radially centered positioning of a rotating shaft, particularly of an operating machine for low temperatures.

United States Patent [1 Doll et al.

[4 1 Dec. 11, 1973 SYSTEM FOR CONTACT-FREE, AXIALLY STABILIZED ANDRADIALLY CENTERED POSITIONING OF A ROTATING SHAFT, PARTICULARLY OF ANOPERATING MACHINE FOR LOW TEMPERATURES [76] Inventors: Robert Doll,Mettinghstr. l, 8

Munich 19; Hartmut Berndt, Konigsteinstr. 11, 8 Munich 13, both ofGermany [22] Filed: July 19, 1972 [21] Appl. N0.: 273,318

[30] Foreign Application Priority Data July 29, 1971 Germany P 21 37850.7

[52] US. Cl. 308/10 [51] Int. Cl. Fl6c 39/06 [58] Field of Search 308/10[56] References Cited UNITED STATES PATENTS 3,110,481 11/1963 Kivenson308/10 X 3,243,238 3/1966 Lyman 308/10 Primary Examiner-James D.Trammell Attorney--Silverman & Cass [57] ABSTRACT A system forcontact-free, axially stabilized and radially centered positioning of arotating shaft, particularly of an operating machine for lowtemperatures.

12 Claims, 3 Drawing Figures PATENTED DEC 1 1 I975 SHEET 2 BF 2 SYSTEMFOR CONTACT-FREE, AXIALLY STABILIZED AND RADIALLY CENTERED POSITIONINGOF A ROTATING SHAFT,

PARTICULARLY OF AN OPERATING MACHINE FOR LOW TEMPERATURES The inventionrelates to a system for contact-free, ax-

ially stabilized and radially centered positioning of a rotating shaft,particularly of an operating machine for low temperatures, comprisingradially centered bearings associated with each shaft end and operatedby magnetic forces, and an electro-magnetic servo mechanism for axialstabilization, whose electro-magnetic device acting axially on the shaftis controlled by a tracer system for the position of the shaft.

Such a positioning system is described in the ETZ.-B. volume 13 (1961,page 525). The bearings associated with the shaft ends are formed byferrite rings. The axial stability is assured by an electro-magneticservo mechanism. There is a disadvangage in this respect that the resetforces occurring in case of a deflection of the shaft are small, so thata precise positioning of the shaft is impossible. Moreover, apositioning system of an electric motor for high numbers of revolutionswith a vertical rotor'shaft is known from the German Auslegeschrift1,219,117, where one shaft end is positioned in a thrust bearing on ahydraulic or pneumatic cushion, while a magnetic centering apparatus inthe form of opposite concentric combs is associated with the other shaftend. This type of positioning system is not a purely magnetic one-Due tothe use of a thrust bearing with a hydraulic or pneumatic bolster such apositioning system cannot be applied at low temperatures.

The invention has the object of creating a magnetic positioning systemfor a rotating shaft which permits a precise and exact positioning ofthe shaft.

Starting out from the initially mentioned magnetic positioning system ofthe prior art, the problem is solved by the invention in that eachradially centered bearing is provided with at least one annular cuttingedge or blade concentrical to the axis of the shaft, connected to theshaft, made of .ferro-magnetic material,

and with a stationary annular blade of ferro-magnetic material, placedopposite at a small. gap, and that both annular blades are located inthe magnetic circuit of a stationary magnet.

The magnetic cutting edge bearings associated with each shaft endproduce at a deflection of the shaft relatively high resetting forces. Arotating shaft can be positioned precisely and exactly as to positionaccording to the invention in connection with an electro-magnetic servomechanism for axialstabilization.

A rotating shaft, particularly an operating machine may be exposed tokindling forces which lead to disturbing movements. Such a disturbingmovement is the precession movement of the shaft. In order to obtain aprecise position in each case, a tracer-controlled electro-magneticsystem exerts a radial force on the shaft to avoid precession movements,the tracer system also responds to radial deflections of the shaft andthe exerted radial power effect of the electro-magnetic system iscoordinated as to position with the determined radial deflection. Thatway it is possible even at the risk of the occurrence of precessionmovements to obtain an exact and precise positioning of a rotatingshaft. Practical expermients have demonstrated that that way very highnumbers of revolutions are attainable which otherwise are unattainablebecause-of the occurring disturbing movements.

Another interfering movement is the rolling movement of the shaftwherein the rotating shaft carries out a circular movement parallel withthe longitudinal axis of the bearingyTo avoid such rolling movements ofthe shaft, the non-rotating parts of the positioning system are heldfirmly, according to another embodiment of the invention, with givenattenuation, and the inherent frequency of the elastic holding means istuned to the inherent frequency of the rolling movement. Particularlythe combination of the magnetic annular blade bearings with the means toavoid movements of precession and rolling of the shaft allows precisepositioning of the shaft even if these kindling or starting forcesshould be exposed to the generation of such interfering movements, evenat maximum revolutions of the shaft. According to another embodiment ofthe invention the stationary annular blade is designed as a polar leg ofthe magnet. The annular blade connected to the shaft end forms an airgap with another polar leg of the magnet.

According to another embodiment of the invention, the gap betweenopposite annular blades is smaller than the gap between the mobileannular blade and the associated polar leg of the magnet.

Preferably the magnet is an axially magnetized permanent magnetsurrounding the shaft end concentrically.

According to another embodiment of the invention the electro-magneticsystem comprises a flange fixed to the shaft, perpendicular to the axisof the shaft and a coil surrounding the shaft ring-like, with an annulariron core U-shaped in cross-section, and the surface of the pole shoeends facing the shaft flange extending obliquely to the axis of theshaft. Such an electromagnetic system generates besides the axiallystabilizing forces also the forces necessary to avoid the interferingmovement. Thus, separate magnetic systems can be avoided.

According to another embodiment of the-invention, the tracer system formaintaining the radial deflection and axial displacement of the shaft isa photo-electric tracer apparatus whose light beam cluster traverses theannular gap between opposite annular blades. Such a tracer system isdirection-oriented so that both the axial movements of displacement ofthe shaft and also the position changes occurring during interferingmovements are taken into consideration. Again separate tracerapparatuses for the individual types of movement are avoided thereby.

The photo-electric cell of the tracing apparatus is preferably connectedto a PD control system to which the winding of the electro-magnet to becontrolled is connected.

Below, the invention is described in detail by means of an embodimentrepresented in the drawing, in which FIG. 1 shows a lateral view of arotating shaft with associated bearings;

FIG. 2 shows a schematic view of the magnetic positioning system of theshaft, and

FIG. 3 shows a schematic view of the holding means of an operatingmachine with the shaft positioning system according to the invention.

The rotating shaft 1 is driven for example by a schematically indicatedturbine wheel 2 or a motor 2. At each of its ends 4 the shaft 1 isprovided with an annular blade 5 of ferro-magnetic material formed bytapered surfaces 6, extending preferably below 45.

Placed opposite, a blade-like annular pole shoe 7 is associatedstationarily to each annular blade 5. An annular permanent magnet 8likewise made of ferromagnetic material is fixedly connected to theannular pole shoe 7 and magnetized in the longitudinal direction of theshaft.

An additional annular pole shoe 9, likewise made of ferro-magneticmaterial is also fixedly connected to the annular permanent magnet 8,the free end of said shoe is arranged opposite the annular surface 10 ofthe annular blade 5.

The annular gap a is to be maintained substantially larger than theannular gap b.

The magnetic system 11 can ally acting magnetic system.

An annular flange 12 of ferro-magnetic material is fastened to or formedat shaft 1. An electro-magnet 13 with a laminated iron core whichannularly surrounds the shaft 1 is associated with one side of flange12. Its pole shoes 14 and 15 are of annular shape and the pole shoesurface 1: x forms an angle of less than 90 with the longitudinal axisof shaft 1.

The electro magnet 13 and the flange 12 form the axbe considered as aradiially stabilizing magentic system which makes it possible inaddition to prevent a disturbing or interfering movement of precession.

The scanning apparatus for determining the axial errors and the errorsadditionally caused by the prescession movement comprises a luminoussource 16, a reversing mirror 17 and a photo-electric cell 18. Thereversing or deflecting mirror 17 is so arranged in the magnetic system11 that the deflected light beam 19 passes through the annular gap b tobe controlled, outwardly via a perforation 48 in the annular magnet 8.The intensity of the exiting light beam is changed by axial faultymovements of shaft 1 and converted into signal changes by thephoto-electric cell 18. These signals are transmitted to a PD controlsystem 20 of known design whose output feeds the coil of theelectro-magnet 13.

ln operating or production machines with a magnetic positioning system arolling movement can occur as additional interfering movement. Therolling movement is a circular movement of the rotor shaft parallel toitself in the rotation-symmetrical field of force. The circumferentialspeed is, here, determined by the mass of the rotor and the radialresetting forces. In order to control such interference movement it ispossible to so design the stationary holding means and so determine itselasticity and attenuation that the inherent frequency of the holdingmeans comes to be located in the proximity of the rolling frequency.

The inherent frequency of the holding means also can be tuned to therolling frequency by applying additional masses. Here, the mass may beapplied directly to the fomration to be tuned, for example, the housing,or via an elastic member, so that the mass determines the inherentfrequency of the entire system via the elastic member.

As shown schematically in FIG. 3, an operating machine 40 with amagnetic positioning system, particularly for low temperatures, isconnected via a pipe 41 of a length l to space-bound formations 42; toavoid any rolling movement, the length 1 of the tube 41 and thus theinherent frequency of the holding means can be tuned to the rollingfrequency. It is also conceivable to effect the tuning of the inherentfrequency of the holding means in relation to the rolling frequency insome other manner, as mentioned above.

We claim:

1. A contact-free, axially stabilized and radially centered positioningsystem of a rotating shaft, particularly of an operating machine for lowtemperatures, comprising radially centered bearings'associated with eachshaft end operated by magnetic forces, and an electromagneticservo-mechanism for axial stabilization whose electro-magnetic systemacting axially on the shaft is controlled by a tracer system for theposition of the shaft characterized by the fact that each radiallycentered bearing is provided with at least one annular cutting blade (5)concentric to the shaft (1) made of ferro-magnetic material, and with astationary annular blade (7) of ferro-magnetic material placed oppositeat a small gap, and that both annular blades are located in the magneticcircuit of a stationary magnet (8).

2. A positioning system, especially according to claim 1, characterizedby the fact that to avoid movements of precession of the shaft 21tracer-controlled electromagnetic system (30) exerts a radial force onthe shaft (1), that the tracer system (16,17,18) responds also to radialdeflections of the shaft and that the exerted radial effect of force ofthe electro-magnetic system, is coordinated in position to thedetermined radial deflection.

3. A positioning system particularly according to claim 1, characterizedin that in order to avoid rolling movements of the shaft at a givenattenuation the nonrotating parts of the positioning system are heldfirmly elastically and the inherent frequency of the elastic holdingmeans is tuned to the inherent frequency of the rolling movement.

4. A positioning system according to claim 1, charac terized by the factthat the stationary annular cutting edge (7) is designed as a polar legof the magnet (8).

5. A positioning system according to claim 1, characterized by the factthat the annular blade (5) connected to the shaft end (4) forms an airgap with another polar leg (9) of the magnet.

6. A positioning system according to claim 5, characterized by the factthat the gap (b) between the opposite annular blades (5,7) is smallerthan gap (a) between the mobile annular blade (5) and the associatedpolar leg (9) of the magnet.

7. A positioning system according to claim 5, characterized in that themagnet (8) is an axially magnetized permanent magnet concentricallysurrounding a shaft end (4).

8. A positioning system according to claim 2, characterized in that theelectro-magnetic system (30) embraces a flange (12) fixed to the shaft(1) perpendicular to the axis of the shaft, and a coil annularlysurrounding the shaft, with an annular iron core of U- shapedcross-section, and the plane (x x) of the pole shoe ends (14,15) facingthe shaft flange extends obliquely to the axis of the shaft.

9. A positioning system according to claim 8, characterized in that thetracer system (16,17,18) for holding the radial deflection and axialdisplacement of shaft (1) is a photo-electric tracer system whosecluster of light beams traverses the annular gap (b) between oppositeannular blades.

nected to the shaft end (4) forms an air gap with another polar leg (9)of the magnet.

12. A positioning system according to claim 6, characterized in that themagnet (8) is an axially magnetized permanent magnet concentricallysurrounding a shaft end (4).

1. A contact-free, axially stabilized and radially centered positioningsystem of a rotating shaft, particularly of an operating machine for lowtemperatures, comprising radially centered bearings associated with eachshaft end operated by magnetic forces, and an electro-magneticservo-mechanism for axial stabilization whose electro-magnetic systemacting axially on the shaft is controlled by a tracer system for theposition of the shaft characterized by the fact that each radiallycentered bearing is provided with at least one annular cutting blade (5)concentric to the shaft (1) made of ferro-magnetic material, and with astationary annular blade (7) of ferro-magnetic material placed oppositeat a small gap, and that both annular blades are located in the magneticcircuit of a stationary magnet (8).
 2. A positioning system, especiallyaccording to claim 1, characterized by the fact that to avoid movementsof precession of the shaft a tracer-controlled electro-magnetic system(30) exerts a radial force on the shaft (1), that the tracer system(16,17,18) responds also to radial Deflections of the shaft and that theexerted radial effect of force of the electro-magnetic system, iscoordinated in position to the determined radial deflection.
 3. Apositioning system particularly according to claim 1, characterized inthat in order to avoid rolling movements of the shaft at a givenattenuation the non-rotating parts of the positioning system are heldfirmly elastically and the inherent frequency of the elastic holdingmeans is tuned to the inherent frequency of the rolling movement.
 4. Apositioning system according to claim 1, characterized by the fact thatthe stationary annular cutting edge (7) is designed as a polar leg ofthe magnet (8).
 5. A positioning system according to claim 1,characterized by the fact that the annular blade (5) connected to theshaft end (4) forms an air gap with another polar leg (9) of the magnet.6. A positioning system according to claim 5, characterized by the factthat the gap (b) between the opposite annular blades (5, 7) is smallerthan gap (a) between the mobile annular blade (5) and the associatedpolar leg (9) of the magnet.
 7. A positioning system according to claim5, characterized in that the magnet (8) is an axially magnetizedpermanent magnet concentrically surrounding a shaft end (4).
 8. Apositioning system according to claim 2, characterized in that theelectro-magnetic system (30) embraces a flange (12) fixed to the shaft(1) perpendicular to the axis of the shaft, and a coil annularlysurrounding the shaft, with an annular iron core of U-shapedcross-section, and the plane (x - x) of the pole shoe ends (14,15)facing the shaft flange extends obliquely to the axis of the shaft.
 9. Apositioning system according to claim 8, characterized in that thetracer system (16,17,18) for holding the radial deflection and axialdisplacement of shaft (1) is a photo-electric tracer system whosecluster of light beams traverses the annular gap (b) between oppositeannular blades.
 10. A positioning system according to claim 9,characterized in that the photo-electric cell (18) of the tracer systemis connected to a PD control system (20), to which the coil of theelectro-magnet (13) to be controlled is connected.
 11. A positioningsystem according to claim 4, characterized by the fact that the annularblade (5) connected to the shaft end (4) forms an air gap with anotherpolar leg (9) of the magnet.
 12. A positioning system according to claim6, characterized in that the magnet (8) is an axially magnetizedpermanent magnet concentrically surrounding a shaft end (4).